The present invention concerns a device for the measurement of exchanges of amounts of heat in non-stationary operational conditions, these conditions having a low level dynamic buried in an environment highly disturbed by important thermal fields, the said device comprising an elongated housing provided with a central cavity, one measuring end and one connection end, the measuring end being closed and the central cavity containing, on the one hand, a measuring cell and, on the other hand, electrical connection members, the said measuring cell comprising at the least one sensitive heat flux measuring element sandwiched between a first heat conducting component and a second heat conducting component.
Such a device allows measuring in real-time of the amounts of heat generated by rheological modifications of material during a transformation thereof, such as for example synthetic material during a plastification process in an extruder or injection machine. The information gathered is significant of the state of the material at a given moment, notably its pressure, its temperature, its viscous flow or, in some housings, its change of phase or its deterioration during another transformation process.
It is well known that the data of sensors, notably data regarding the temperature, the pressure and the viscosity are likely to supply information on the state of the material, but it is complex to obtain, in real-time, comprehensive local information on the Theological state of this material in the course of transformation at a given moment.
One knows from experience that all this information can be supplied by sensors referred to as thermal flux sensors using an appropriate computer processing of the signals delivered by these sensors. The physical amounts cited previously are all translated by exchanges of amounts of heat, i.e. that any rheological phenomenon where one can express the evolution as a thermal quantity is detectable.
Most of the existing heat flux sensors have been designed to measure mainly flux of the heat balance type representative of heat exchanges between material and its environment. As the heat flux generated in the heart of the material at the time of local rheological modifications are very low as compared with the flux from exchanges with the environment, they are therefore drowned in a signal of considerable level which must be processed in order to be able to extract the required information. This is a complicated and costly method and it appears complex to include at the present time such devices in an industrial process so as to operate a control on-line.
Now, for this type of application, it is the dynamic of transformations of the material, which, is essential and not the heat balance. This is why a thermal flux sensor has been developed meeting these requirements and which has been the subject of the international patent application published under the number WO 00/08431 and entitled xe2x80x98Measurement device for exchanges of amounts of heat in unsteady, non-stationary or transient operational conditionsxe2x80x99.
This device comprises a measuring cell having at least one thermal flux sensitive element sandwiched between a first heat conducting component and a second heat-conducting component. The measuring cell comprises a flat circular base which is held in contact by mechanical compression means against the inner surface of the bottom of a body in which is arranged the measuring cell.
Due to this, the two components which hold the said sensitive element sandwiched are in direct contact with the body of the device which is itself linked to the environment of the material to be controlled. The result is that this device is fitted to measure the exchanges of amounts of heat between the material to be controlled and its immediate environment. As an example, the device is capable of measuring the exchanges of amounts of heat between the outer sheath of an injection-moulding machine and the synthetic material itself in the course of transformation, which flows inside this sheath in molten state. It is obvious that heat exchanges occur continuously between the material and its immediate environment in such a way that the measurements carried out by this device do not allow control over the evolution of the material during plastification in the area where the material is in a molten state, in an efficient and reliable manner.
The present invention intends to obviate these disadvantages by facilitating making an accurate check on the evolution of the material during its transformation through a simple measurement of exchanges of amounts of heat corresponding no longer to exchanges due to flux resulting from the heat balance between the material and its environment, but exclusively to local exchanges between the material and a reference heating device.
This object is achieved by the device such as defined in the preamble and characterized in that the said first heat conducting component is in contact with at the least one surface of the said housing, and in that the said second heat conducting component is insulated from the said housing and constitutes a constant heat capacity.
Due to this fact, the thermal flux type sensitive element is arranged between the said first component, which constitutes a heat electrode in contact with the environment to be controlled, and the said second component, which constitutes a specified heat capacity.
Through these means, one measures exchanges of amounts of heat, no longer between the material to be controlled and its immediate environment, but between the material to be controlled and a reference heat capacity perfectly specified, built into the measuring cell and heat insulated from the housing of the device.
When a local rheological modification occurs within the material represented by an absorption, restoration or production of energy in heat form, amounts of heat are exchanged with the heat capacity of the measuring device by flowing through the thermal flux sensitive element. The amounts of heat are stored in the heat capacity of the device, where the temperature rises up until it is balanced with the temperature of the local material.
When the phenomenon is no longer exothermic but endothermic, the heat capacity of the device, in reverse, sheds the amounts of heat which are exchanged with the material through the thermal flux sensitive element, up until the next local thermal equilibrium.
The dynamic of these local heat exchanges is detected by the thermal flux sensitive element which generates an electric signal significant of these exchanges, in real-time.
The electric signal obtained is non-stationary. It supplies information in real-time, on the dynamic of local rheological modifications of the material, in an environment highly disturbed notably by exchanges of thermal energy at very high level between the material and its environment.
According to a preferred embodiment, the measuring end of the housing is slightly flat and one of the ends of the said first heat-conducting component is at least partially in contact with an inner surface of the said measuring end.
Conveniently, the said first heat-conducting component comprises a heel provided with a contact surface the shape and dimensions of which correspond to that of an inner surface of the said measuring end.
According to an initial embodiment, the said contact surface of the said heel of the said first heat-conducting component is circular.
According to a second embodiment, the measuring end of the housing is slightly tapered and one of the ends of the said first heat-conducting component is at least partially in contact with an inner surface of the said measuring end.
According to this second embodiment, the said first heat conducting component comprises a heel provided with a contact surface, this contact surface being up against an inner surface of same geometry as the said tapered measuring end.
Preferably, the thermal flux sensitive element as well as the said first heat conducting component and the said second heat conducting component are coated with a layer of gold, at least on their mutual surfaces, so as to ensure, through diffusion of the layer of gold, a close heat conductive contact between the components involved.
According to a particularly simple, efficient and convenient construction, the housing comprises, on the side of its measuring end, a hollow finger where the thickness is reduced as compared with the rest of the body so as to present a considerable axial thermal resistance, the measuring cell being necessarily housed in this finger.
The measuring cell is preferably maintained at the bottom of the hollow finger through means of compression fitted to ensure flattening of the said first heat conducting component against the inner surface of the measuring end.
According to a particularly interesting construction, the right section of the hollow finger is circular, the said first heat conducting component has a semi-cylindrical section where the diameter is almost equal to the diameter of the inner surface of the hollow finger, and the second heat conducting component has a semi-cylindrical section where the diameter is smaller than the diameter of the inner surface of the hollow finger.